At the time of the appearance of the resurrected Jesus Christ to the Nephites, the multitude went forth, felt the resurrected body of the Savior, and testified that ‘it was he, of whom it was written by the prophets, that should come’ and then cried out ‘with one accord, saying: Hosanna!’ (3 Nephi 11:15–16.)
The word Hosanna is a transliteration of a Hebrew word of supplication which means in essence ‘Oh, grant salvation.’ Evidently the people were asking the Savior to teach them the way to salvation; thus it is not surprising that he immediately teaches them the basic principles and ordinances of the gospel.
(Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, p. 261-62)